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Mechanical properties and fractal morphology of HIPS/SBS blends

Blends from high impact polystyrene (HIPS) and polystyrene-b-polybutadiene-b-polystyrene block copolymers (SBS) (thermoplastic elastomers, Kraton D1101) are studied with recycling in view. Binary systems HIPS/ SBS elastomer containing up to 85 % of SBS elastomer were investigated. Samples were prepared by melt mixing in a Haake twin-screw extruder and were injection molded into plates on a Zwick injectometer. The blends were characterized by measuring dynamic mechanical properties, creep and recovery) and by defining morphology. Increasing the SBS content one observes a vanishing PS-related brittle type of fracture, while an SBS-related ductile fracture emerges. Best mechanical properties are obtained for blends HIPS/SBS 90/10. The heterogeneous blends exhibit a two-phase morphology. This structure is investigated by scanning electron microscopy (SEM) and compared to mechanical and processing properties as a function of SBS content. The topography images of polymer blend fracture surfaces were processed using the fractal analysis software to obtain the fractal indicies of the surfaces. The average (classical) fractal index was less than two for the fracture surfaces of polystyrenic (HIPS/SBS) blends. These fractal results were correlated with the blend mechanical properties and with the Hurst exponent, obtained from the time series of processing parameters (torque, melt pressure). Hence, it is considered that the processing and mechanical results are in good agreement with the fractal properties of the fracture surfaces even for heterogeneous polymeric blend materials.

high impact polystyrene; styrene/butadiene/styrene; PS-HI/SBS blends; torque; creep; recovery; fractal index; fracture surface

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